1. Field of the Invention
The present invention relates to a chassis for an illuminating unit, and an illuminating unit, a display device and a television receiver incorporating the chassis, and specifically relates to a chassis for an illuminating unit preferably applied to a display device or a television receiver having a translucent liquid crystal display panel, and an illuminating unit, a display device and a television receiver incorporating the chassis.
2. Description of the Related Art
Among flat-screen display devices, for example, a liquid crystal display device and other devices including a translucent liquid crystal display panel generally includes an illuminating unit placed behind the liquid crystal display panel. The illuminating unit includes a light source and optical sheets, controls the properties of light emitted from the light source using the optical sheets, and projects the light toward a back surface of the liquid crystal display panel. The light projected from the illuminating unit passes through the liquid crystal display panel, making an image displayed visible on a front surface of the liquid crystal display panel.
The optical sheets are interposed between the light source and the display panel, so that if the optical sheets suffer wrinkles or deformed portions, luminance irregularity or a shade caused by the wrinkles or the deformed portions appears on the liquid crystal display panel in some cases. Accordingly, it is necessary to keep the optical sheets in a state of having no wrinkle or deformed portion thereon in order to provide a display device that achieves high-definition image display.
Examples of a structure for supporting the optical sheets include a structure for supporting the optical sheets with through-holes provided at edge portions thereof, and into the through-holes, bosses are loosely fitted (see Japanese Patent Application Unexamined Publication No. Hei11-337942) and a structure for supporting the optical sheets with positioning pieces extending at the edge portions thereof, and the positioning pieces are engaged into concave portions provided on a chassis or a frame (see Japanese Patent Application Unexamined Publication No. 2001-76527). According to the above-described structures, the optical sheets can be positioned and held so as not to fall off a predetermined area.
However, with the above-described structures, if the display device is used in an upright position, the optical sheets are subjected to their own weight at the peripheries of the through-holes or the positioning pieces. As a result, there is a possibility that the peripheries of the through-holes or the positioning pieces suffer wrinkles or deformed portions. Accordingly, it is preferable that the optical sheets are supported with any one of their sides along their entire length.
FIG. 6 is an exploded perspective view schematically illustrating a structure of a conventional display device in which optical sheets are supported with all the sides there around along almost their entire lengths. A display device 9 includes optical sheets 92 interposed between a display panel 96 and lamps 95 as a light source. A brief description only relating to supporting of the optical sheets 92 in the display device 9 will be provided. The optical sheets 92 are arranged so that edge portions thereof are on support surfaces 911 provided at edge portions of a chassis 91 and side holders 94, and a frame 93 is attached thereto from the front side. Stand walls 912 protruding toward the frame 93 are provided at outer sides of the support surfaces 911 of the chassis 91. Meanwhile, different-level surfaces 931 lowered toward the chassis 91 or the side holders 94 are provided at the inner edges of the frame 93. Then, the frame 93 is incorporated into the chassis 91 so that the different-level surfaces 931 fall in areas surrounded by the stand walls 912. Accordingly, the edge portions of the optical sheets 92 fit areas surrounded by the support surfaces 911 and the stand walls 912 of the chassis 91 or the side holders 94, and the different-level surfaces 931 of the frame 93.
If the display device 9 is used in a state of standing with its longer side placed as the lower side, the optical sheets 92 are apt to move downward due to their own weight so as to be brought to a state of being supported with the lower side thereof in contact with the stand wall 912 of the chassis 91. As described above, the optical sheets 92 are supported with their entire lower side, preventing the optical sheets 92 from being subjected to their own weight at a certain portion thereof.
However, if there is a gap between the chassis 91 and the frame 93, the lower side of the optical sheets 92 could get into the gap and the optical sheets 92 suffer deformation in some cases.
To prevent the optical sheets 92 from getting into the gap between the chassis 91 and the frame 93 and from suffering the deformation, narrowing or eliminating the gap between the stand wall 912 of the chassis 91 and the different-level surface 931 of the frame 93 can be considered. However, in order to place the different-level surfaces 931 of the frame 93 so as to fall into the areas surrounded by the stand walls 912 of the chassis 91, dimensional tolerance needs to be established to some extent in design, and narrowing the gap makes it difficult to place the frame 93. Further, it is necessary for the gap to accommodate a difference in volumes of deformation such as thermal deformation of the respective members. Accordingly, it is extremely difficult to narrow or eliminate the gap, realistically.
Meanwhile, examples of a structure for supporting optical sheets with all of their sides along the entire lengths include a structure for securing the optical sheets with their four sides so as to be surrounded from the front side and the back side and a structure for adhering the optical sheets with all of their sides to the frame or the chassis with double-faced tapes. These structures prevent the optical sheets from moving or from suffering deformation by securing all of their sides of the optical sheets, thereby preventing occurrence of wrinkles or deformed portions on the optical sheets. However, such structures have the following problems.
In the structure for securing the optical sheets with their four sides to the frame or other members, if thermal expansion occurs to the optical sheets and the frame due to heat generation in use and other reasons, forces are applied to the four sides of the optical sheets, the forces being unexpected due to a difference in coefficients of the thermal expansion of the optical sheets and the frame. As a result, the four sides of the optical sheets may suffer wrinkles or deformed portions. For example, a coefficient of thermal expansion of a synthetic resin material is generally higher by one digit or more than that of a metal material. Accordingly, if the optical sheets are made from the synthetic resin material and the frame is made from the metal material, the portions of the optical sheets with which the optical sheets are secured to the frame are prevented from thermally expanding during the time the temperature rises. Accordingly, the boundary between the portions with which the optical sheets are secured to the frame and portions with which the optical sheets are not secured to the frame develops a difference in deformation volumes, and the vicinity of the boundary results in occurrence of wrinkles or deformed portions.
Hence, a structure for supporting the optical sheets with all of their sides along the entire lengths while restraint on the respective sides is minimized is desired. However, if all the sides of the optical sheets are not restrained, the above-described problems arise and occurrence of wrinkles or deformed portions cannot be prevented.